The present disclosure relates to environmental control systems. More specifically, the present disclosure relates to drain holes in a ram air fan assembly for an environmental control system.
An environmental control system (“ECS”) aboard an aircraft provides conditioned air to an aircraft cabin. Conditioned air is air at a temperature, pressure, and humidity desirable for aircraft passenger comfort and safety. At or near ground level, the ambient air temperature and/or humidity is often sufficiently high that the air must be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, ambient air is often far cooler than desired, but at such a low pressure that it must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressurized air sufficiently that it must be cooled, even if the ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the ECS before the air is delivered to the aircraft cabin. As heat is removed from the air, it is dissipated by the ECS into a separate stream of air that flows into the ECS, across heat exchangers in the ECS, and out of the aircraft, carrying the excess heat with it. Under conditions where the aircraft is moving fast enough, the pressure of air ramming into the aircraft is sufficient to move enough air through the ECS and over the heat exchangers to remove the excess heat.
While ram air works well under normal flight conditions, at lower flight speeds, or when the aircraft is on the ground, ram air pressure is too low to provide enough air flow across the heat exchangers for sufficient heat removal from the ECS. Under these conditions, a fan within the ECS is employed to provide the necessary airflow across the ECS heat exchangers. This fan is called a ram air fan. The ram air fan includes an electric motor with a motor rotor that rotates about a shaft. The ram air fan also includes a number of associated rotating components, such as a fan rotor, to pull air into the ram air fan. The electric motor and the associated rotating components generate heat in the ram air fan that is cooled with a cooling air flowing through the ram air fan. Condensation can form in the ram air fan due to mixing of the heat from the motor and associated rotating components, the cooling air flowing through the ram air fan, and the environment in which the ram air fan is located. This condensation can cause problems with the operation of journal bearings in the ram air fan, potentially causing them to fail. This condensation can also cause failure of the electric motor. Failure of the journal bearings and/or the electric motor can cause overall failure of the ram air fan.